Carbonate-hosted Ore Research Articles

Enrichment of Se-Te-Au in the Jilongshan Au-Cu Skarn Deposit, Hubei Province: Insight from Pyrite Texture and Composition

Selenium and Te are two important critical metals, which are often produced as by-products in Au-Cu deposits related to magmatic–hydrothermal systems, such as porphyry and skarn deposits. The Jilongshan Au-Cu deposit is a typical skarn deposit located in the middle and lower parts of the Yangtze River metallogenic belt. Previous studies show that it has valuable Se and Te resources, but their occurrence, particularly the relationship between the texture and composition of pyrite, and the enrichment mechanism of Se, Te, and Au remain unclear. Here, the textures and the major and trace elements of the Jilongshan pyrites were studied by using an optical microscope, EMPA, and LA-ICP-MS to reveal the occurrence of Se, Te, and Au in pyrite, as well as their genetic links with the pyrite mineralogical signature. The results show that there are three types of ores in the Jilongshan deposit, including granite porphyry-hosted, skarn-hosted, and carbonate-hosted ores. All of these ores contain major amounts of pyrite, which can be divided into four different generations. The first generation of pyrite (Py1) belongs to sedimentary genesis with a typical framboid texture and its Co/ Ni ratios are less than 1, whereas Py2, Py3, and Py4 belong to hydrothermal genesis and their Co/ Ni ratios are between 1.0 and 30.2. Selenium concentrations in Py2 and Py3 are relatively high (median, 138 ppm and 344 ppm, respectively), which are mainly present as isomorphism and a small amount as selenite in pyrite. Compared with granite porphyry-hosted and skarn-hosted ores, pyrite from carbonate-hosted ores has the highest Se concentrations. The latest generation of pyrite (Py4) contains the highest concentrations of Te (average, 140 ppm) and Au (average, 12 ppm) among the hydrothermal pyrites. Therefore, the precipitation of Se mainly occurs in pyrite during the early high-temperature stage, whereas higher concentrations of Te and Au are mainly enriched in pyrite during the late stage with low temperatures.

Hypogene speleogenesis related to porphyry magmatic intrusions and its influence on subsequent karst evolution in the Peruvian high Andes

Carbonate rocks of Cretaceous and Jurassic age are widespread in the Peruvian Andes where they host numerous magmatic intrusions and related ore deposits. Most of Peru's metal ore deposits are located at high elevations within a narrow, tectonized carbonate-rock belt extending over 2000 km in length. Many of the limestone formations are karstified and characterized by high recharge and percolation rates, well-developed subsurface drainage and complex flow patterns. Knowledge of karst in the Andes is generally limited, although karst is recognized to cause extreme hydrogeologic complexity and great challenges in development of mining facilities located in carbonate settings. Aspects of the origin of void/conduit systems (i.e. speleogenesis) and karst evolution are rarely addressed in environmental impact and risk assessment studies.This study in the Antamina area in the east side of the Cordillera Occidental, home to the world largest known skarn copper‑zinc deposit, demonstrates that the current karst system has formed as the result of polygenetic and multi-phase development. Structure-controlled hypogene cave systems are well-preserved and widespread in the area and present a foremost example of endogenous hypogene speleogenesis related to magmatic intrusions. Hypogene karst structures have strongly influenced subsequent epigene karstification, which commenced at the Pliocene-Pleistocene boundary. Changes in the base-level position due to the landscape evolution and Pleistocene glaciations were major additional factors that influenced epigene karst development. The findings of this study are potentially relevant to assessing karst origin and hydrogeology in many carbonate-hosted ore deposits in the Peruvian Andes and other regions. This study shows that the speleogenetic and evolutionary approach is indispensable in the development of sound conceptual models of groundwater flow in karst terrains and the assessment of karst-related hazards and risks.

Origins and mixing contributions of deep warm groundwater in a carbonate-hosted ore deposit, Sichuan-Yunnan-Guizhou Pb-Zn triangle, southwestern China

Sichuan-Yunnan-Guizhou (SYG) carbonate-hosted Pb-Zn triangle is a world-class metallogenic belt and classified as Mississippi Valley-Type (MVT), which provides the greatest ore production in China. However, little is known about the effects of water-rock interactions involving the ore deposits and the modern hydrologic system. Measured chemical and isotopic compositions of the deep groundwater are used to evaluate water origins, potential circulation depth, reaction temperatures, and mixing process with shallow groundwater to assess possible linkages between regional hydrogeology and ore deposits. Within the Maoping sub-deposit, deep groundwater is warmer (21.2–32.0 °C), has lower pH, higher HCO3− and SO42− concentrations, higher average 87Sr/86Sr ratio (0.7148) and Sr concentration (4.1 mg/L), more positive δ13CDIC values (−4.5 to −4.2‰), and lighter average isotopic value (δD = −98 and δ18O = −13.7‰) relative to shallow groundwater, suggesting an origin distinct from modern surface recharge. The light isotopic composition of the deep warm water indicates recharge at a cooler temperature in the past, perhaps during the Last Glacial Maximum. The δ13CDIC values reflect isotopic equilibrium between deep groundwater and surrounding rocks along with a possible deep source of CO2. The oxidation process of sulfides, including H2S and pyrite linked to the ore-forming processes, could produce sulfuric acid that enhances carbonates dissolution and generates elevated HCO3− and SO42− concentrations. Reaction temperatures for the deep groundwater appear to have been around 50–65 °C based on quartz geothermometers and given a regional geothermal gradient of 24.1 °C/km suggest reactions occurred at depths ~1900 m below the land surface. Elevated Sr concentrations with radiogenic Sr isotope ratios reflect reaction with basement rocks and carbonates during the deep circulation. Sr concentration and isotope mixing models demonstrate different recharge sources and suggest the contribution of deep warm groundwater captured in mine drainage. These results reflect the importance of deep groundwater circulation and reactions in a large ore deposit that may improve understanding of potential effects of these important ore bodies on regional water compositions in the SYG triangle and other MVT ore deposits.

Studies on lowering of uranium from mine water by static bed ion exchange process

ABSTRACTThis paper gives results of the studies carried out for lowering of U content in mine water of a carbonate-hosted uranium ore deposit using static bed ion exchange technology with an emphasis on using chemicals benign to the environment and operating plant. The mine water contained 2 mg/L of U. The limiting concentration of U for safe discharges fixed by the World Health Organisation (WHO) is ≤ 0.03 mg/L. The investigations carried out include screening of various commercial strong base anion exchange resins for the duty condition followed by optimization of operating parameters during loading and elution with ‘screened-in resin’. Modeling of the U sorption on the resin was also carried out. A commercial strong base anion exchange resin namely PFA 4759 satisfied the desired conditions for safe discharges. PFA 4759 gave good loading capacity of about 28 g of U per litre of wet settled resin, when the counter-ion was bicarbonate anion with 50 bed volume/h of mine water as volumetric throughput. Elution studies with strong bicarbonate solution (1M) indicated the scope of recovering 99% of the loaded U. The adsorption followed the Langmuir model with pseudo-second-order kinetics.

Potential of Critical High-technology Metals in Eastern Alpine Base Metal Sulfide Ores

The chemical composition of Zn‑, Cu and Fe sulphides in base metal mineralizations of the Eastern Alps was investigated using laser ablation-ICP-MS methods, with a focus on the concentration of high-technology, critical metals. A total of more than 6300 in-situ analyses were carried out on 311 polished sections representing 27 individual mineralizations. These comprise carbonate-hosted Pb-Zn deposits of the Bleiberg-type, stratiform deposits in Paleozoic metasediments and metavolcanic rocks (e. g. Arzberg, Walchen) and vein-type mineralization (e. g. Koprein, Metnitz). Two sphalerite types emerge: type (1) is poor in Fe (<1%), Mn, Co, Ga, In, Sn, Sb, but significantly enriched in Ge (up to >500 ppm), As, Tl and Pb; it is restricted to carbonate-hosted non-metamorphosed sediments. (2) Sphalerite elevated in Fe, Co, Ni, Cu, Ag, In and Sn in stratiform and vein-type ores hosted by Paleozoic low to medium grade metamorphic rocks. Large variations exist among both groups, and unusual compositions were also encountered, e. g. vein-type ores showing a Ge-Sb-Co association at Metnitz, Gurktal nappe. Chalcopyrite associated with type (2) sphalerite may have high Ag and In concentrations. Pyrite and pyrrhotine are carriers of Co, Ni and As. The highest potential for Ge is associated with carbonate-hosted ores in the Drauzug and Karawanken Mountains. For Co and In, low potentials are associated with some of the larger stratiform mineralizations.

Zebra textures in carbonate rocks: Fractures produced by the force of crystallization during mineral replacement

Zebra textures are enigmatic banded fabrics that occur in many carbonate-hosted ore deposits, dolomite hydrocarbon reservoirs and carbonate successions globally. They consist of a variety of minerals and are characterised by parallel light and dark bands that occur at a millimetre- to centimetre-scale. Based on petrological evidence, there is general consensus that the dark bands formed by replacement of the carbonate host rock. Historically, more contention surrounds the origin of the light bands, but the dominant view is that these are mineral-filled cavities, which is supported by overwhelming textural evidence. Overall, the feature common to all versions of zebra textures is mineral replacement of the original carbonate host.We suggest that mineral replacement (and the force of crystallization) in association with open space generation is a viable mechanism for the development of zebra cavity systems. Dissolution and open space generation in either evaporites or carbonates adjacent to the site of replacement reactions is necessary to remove the confining pressure from the rock and to allow the development of fractures. The pressure of the growing replacement crystals within the carbonate pervasively splits the carbonate apart, producing thin strips of carbonate surrounded by open space. The fractures may then be subject to dissolution and are later filled by cements. Very regular stratabound zebra textures (as found in ore deposits like Cadjebut, Australia and San Vicente, Peru) may be related to stratabound dissolution (of evaporites or carbonates), whereas irregularly distributed zebra textures are more likely to be associated with irregular carbonate dissolution.

Quantitative mineralogical analysis of European Kupferschiefer ore

Kupferschiefer samples from five distinct deposits in Germany and Poland were studied with the aim to quantitatively determine their mineralogical composition using complementary approaches. Their inherently extremely fine-grained matrix, sheet silicate-dominated mineralogy, and highly variable copper sulphide content in the presence of organic components, render quantitative mineralogical analysis difficult. In an attempt to develop a comprehensive yet feasible analytical routine for Kupferschiefer black shale and associated sandstone- and carbonate-hosted ores, analytical techniques were tested and adapted to suit this purpose. This study focuses on a combination of mineralogical approaches using quantitative X-ray diffraction (XRD) and image-based automatic mineral liberation analysis (MLA). Quantitative bulk-powder XRD was achieved by Rietveld refinement, based on phase identification and selection of suitable structural models. The identified minerals were verified with scanning electron microscopic measurements coupled with energy dispersive X-ray spectroscopy (EDX) and optical microscopy. Results of QXRD and MLA were compared to chemical assay data. It is concluded that MLA and QXRD deliver satisfactory results for this complex raw material, but only when used in combination. When used independently, XRD and MLA are susceptible to significant errors related especially to sample preparation, mineral misidentification and quantification. To assure a successful quantitative mineralogical description of complex raw materials or processing products it is thus strongly recommended to verify all mineralogical information by independent analytical techniques – and to validate quantitative mineralogical information with quantitative chemical data.

Mobilization of Mercury and Arsenic from a Carbonate-hosted Ore Deposit, Central Idaho, U.S.A.

The Cinnabar and Fern mine sites in central Idaho are primary source areas for elevated mercury and arsenic entering the South Fork of the Salmon River, which provides critical spawning habitat for bull trout and Chinook salmon. Mercury mineralization is hosted by carbonate rocks, which generate waters dominated by Ca2+ and HCO3− at pH 7 to 9. A synoptic sampling was conducted on headwater tributaries to determine geologic background concentrations and quantify trace metal concentrations in stream water associated with historical mining. Geologic background concentrations in unfiltered Cinnabar Creek water were 8 - 14 ng Hg L-1 and 4.8 - 9.5μg As L-1. Immediately downstream from the mine site, concentrations increased to 257 ng Hg L-1 and 20.6μg As L-1. Groundwater inflow diluted these concentrations by approximately half before the confluence of Cinnabar Creek with Sugar Creek. As expected, mercury and arsenic concentrations increased downstream in Sugar Creek below the confluence with Cinnabar Creek. However, the final downstream reach on Sugar Creek showed an increase in unfiltered mercury, methylmercury, and iron concentrations relative to the upstream reach. This increase is associated with historical mining activity in a mineralized area of carbonate rock that intersects the reach.

Geochronologic (Re[sbnd]Os) and fluid-chemical constraints on the formation of the Mesoproterozoic-hosted Nanisivik Zn[sbnd]Pb deposit, Nunavut, Canada: Evidence for early diagenetic, low-temperature conditions of formation

The age and origin of the past-producing Nanisivik carbonate-hosted ZnPb deposit in Nunavut, Canada, have been controversial for decades. Various direct and indirect dating methods have produced results ranging from Mesoproterozoic to Ordovician in age, and previous studies of the mineralising fluids have suggested that the fluids were anomalously hot (>150°C). This study combines ReOs (pyrite) geochronology, in-situ sulphur isotope analysis, and fluid inclusion analysis to refine both the timing of mineralisation and the nature of mineralising fluids. ReOs pyrite analysis shows that the Nanisivik deposit formed ca. 1.1Ga, broadly similar to the depositional age of the host rock and with the Grenville orogeny, making it one of few known Precambrian carbonate-hosted ZnPb deposits. In-situ sulphur isotope measurements from Nanisivik show a narrow δ34S range of 27.54±0.72, very similar to what has been reported before in bulk sample analyses. New fluid inclusion data show that the mineralising fluids were ~100°C, which is not anomalous in the context of carbonate-hosted base-metal deposits. The fluids exhibit no significant spatial variation in homogenisation temperature in the 2-km-long ‘upper lens’ of the ore deposit, but recrystallisation and modification of fluid inclusions took place in the immediate vicinity of the cross-cutting ~720Ma “mine dyke”. The deposit is broadly inferred to have formed during late Mesoproterozoic assembly of supercontinent Rodinia, when regional hydrostatic head developed under the influence of far-field stresses originating in the developing Grenville orogen. The Nanisivik deposit remains anomalous only in its age; most other aspects of this ore deposit are now shown to be quite typical for carbonate-hosted ore deposits.

Upper Cretaceous carbonate hosted zinc–lead–barite deposits in Northern Thrust Zone, northern Iraq: petrography and geochemistry

Zinc–lead–barite deposits located in Lefan and Lower Banik localities of about 25 km northeast of Zakho City, Northern Iraq consist of a group of strata-bound sulfides hosted in Upper Cretaceous (Upper Campanian–Maastrichtian) dolomitic limestone. Carbonate-hosted ores contain 3.77% Zn, 2% Pb, and 5% Fe, while in lower Banik, they contain 1.5% Zn, 0.37% Pb, and 1.4% Fe. Diagenetic processes, such as dolomitization and recrystalization in addition to the type of microfacies, provided appropriate physical and chemical conditions that permitted the passage of ore-bearing fluids and participated in precipitation and ore localization. These deposits are precipitated in a platform and developed within the Foreland Thrust Belt. Ore precipitated as infill of intergranular dolomite porosity with replaced dolomite and rudist shells forming disseminated crystals that occupy intergranular pore spaces around dolomite and calcite and as infill of dissolution spaces and fractures.

Stable isotope geochemistry of carbonate minerals in supergene oxidation zones of Zn–Pb deposits

The 18O/ 16O and 13C/ 12C ratios of carbonate minerals formed by supergene oxidation of Zn–Pb deposits and submarine alteration of ancient slags were studied in order to constrain isotope fractionation factors for smithsonite, cerussite, and phosgenite, and to characterize conditions of nonsulfide ore formation. We present new isotope data of carbonate-hosted ores from the Iglesiente district (Sardinia, Italy) and Vila Ruiva (Portugal), as well as from the silicate-hosted ores of the Broken Hill district, New South Wales (Australia) and Freihung (Germany) and review previously published isotope data. The temperature dependence of oxygen isotope fractionation between Pb and Zn carbonate minerals and water below 240 °C for cerussite and below 100 °C for smithsonite and phosgenite can be expressed as 1000ln α cerussite–water = 2.29(10 6 / T 2) − 3.56 1000ln α smithsonite–water = 3.10(10 6 / T 2) − 3.50 1000ln α phosgenite–water = 2.55(10 6 / T 2) − 3.50 with T in Kelvin. The carbon isotope fractionation between smithsonite, phosgenite, hydrozincite and calcite is less than about 2‰, while cerussites are strongly depleted in 13C by about 10‰ as compared to the former minerals. Oxygen isotope variations of individual carbonate minerals within a deposit are relatively small indicating constant formation temperatures and a single, meteoric fluid source. Average formation temperatures of the studied deposits are calculated at 20 ± 5 °C using the estimated isotope compositions of local paleometeoric waters. We observe a linear relationship between the isotope values of estimated paleometeoric waters and supergene carbonates. Thus, base metal carbonate minerals from supergene deposits may provide paleoclimatic information. The carbon isotope values are in most carbonate-hosted deposits highly variable (more than 10‰) suggesting at least two isotopically distinct carbon sources. The isotopically light component can be related to oxidation of C3 plants (soil-derived carbon) and/or microbes that take active part in sulfide oxidation, while the isotopically heavy component originates from carbonate carbon from wall rocks and/or atmospheric carbon. The 13C-enriched component is less dominant in silicate-hosted deposits.

Formation of Willemite in Hydrothermal Environments

Willemite (zinc silicate) is the main zinc mineral in some carbonate-hosted ore deposits (e.g., Franklin, New Jersey; Vazante, Brazil; Beltana, South Australia; Kabwe, Zambia). Recent interest in these unconventional zinc deposits has increased because of high zinc grades that exceed 40 wt percent, relatively low environmental impact of ore processing owing to the lack of acid-generating sulfides in the waste, and advances in ore processing technologies. In the past, most metallogenic studies proposed formation of willemite deposits by supergene or hypogene alteration of preexisting sulfide deposits. However, recent data on the Vazante, Beltana, and Kabwe deposits indicate willemite crystallization at temperatures in excess of 150°C, raising the possibility of primary precipitation from hydrothermal fluids. We use numerical geochemical modeling to examine the formation of willemite under hydrothermal conditions. Activity-activity diagrams reveal that, in the presence of dissolved sulfur and quartz, willemite instead of sphalerite will precipitate under oxidizing (e.g., hematite-stable, sulfate-predominant) and alkaline (pH higher than K feldspar-muscovite-quartz) conditions. Willemite also becomes more stable, relative to sphalerite, at high temperature, and willemite can coexist with magnetite at 300°C. The stabilities and solubilities of sphalerite, willemite, smithsonite, hydrozincite, and zincite were calculated for wide ranges of temperature (25°–300°C), chloride concentration, dissolved sulfur and carbon concentrations, pH, quartz saturation, and oxidation potential. Plots of the solubility of the different minerals as a function of two variables (e.g., temperature and redox state; pH and redox state) allow us to predict the effects of changing chemical conditions, which in turn permits an estimate of the efficiency of particular precipitation processes. Cooling is an effective process for precipitating sphalerite but not willemite, whereas pH increase (e.g., by acidic fluids reacting with carbonates) is effective for precipitating willemite but not sphalerite. Dynamic geochemical models that simulate physicochemical processes are used to understand the formation of the Beltana willemite deposit in the Adelaide geosyncline of South Australia. This small, high grade deposit (850,000 t at 36% Zn) is hosted in dolomite of the Cambrian Ajax Limestone, next to a tectonic contact with the diapiric, halite-bearing clastic sediments of the Callanna Group. The orebody is associated with hematite alteration and is characterized by the total absence of sulfides; willemite is the only zinc ore mineral, and the arsenate hedyphane (Ca 2 Pb 3 [AsO 4 ] 3 Cl) is the main lead mineral. The model results show that willemite will precipitate in response to water-rock interaction and fluid mixing processes at temperatures above 120°C. The presence of arsenate in the hydrothermal fluid is likely to have been important at Beltana; in arsenate-absent models sulfate is reduced to sulfide by the precipitation of ferrous iron as hematite, resulting in the precipitation of sphalerite and galena. In contrast, in models including arsenate the reduction of sulfate to sulfide is inhibited and willemite is predicted to precipitate.

華南における２・３のマグマ- 熱水性鉱床の硫黄の起源

Mill concentrates of ore sulfides from three magmatic-hydrotherml ore deposits were stud- ied for δ 34 S at the granite-hosted Xihuashan deposits, and carbonate-hosted Shizhuan and Huashaping deposits. These ore deposits occur in the South China Fold System, which is composed of mid-Paleo- zoic miogeosynclinal sediments dominant in carbonates toward the Devonian age. Averages of the ore sulfides are -0.9 permil for the Xihuashan, +7.0 permil for the Shizhuan and +13.2 permil for the Huashaping deposits. Endogranitic ore sulfur of the Xihuashan and the Shizhuan deposits are consid- ered magmatic, derived from by ca.+2 ‰ δ 34 S granitic magma, but the carbonate-hosted ore sulfurs at the major part of the Shizhuan and Huashaping deposits are much higher than those expected from rock sulfur δ 34 S values of the Yanshanian granites of the South China Fold System. Thus, addition of 34 S-enriched sulfur into the ore solutions is considered. Devonian and Carboniferous carbonates of the South China Fold System are very high in the δ 34 S values of structurally substituted sulfate (SSS) sulfur, averaged as +25.7 and +15.7 permil, respec- tively, which are higher than the reported values from other areas of these ages. The SSS contents of the Paleozoic carbonates are very low at present, but recent carbonates contain typically 0.1 to 1 % equivalent sulfate. The very low SSS contents in the wall rock carbonates and high δ 34 S values in the ore sulfides may have been resulted from carbonate SSS extracted during recrystallization and some- how mixed with magmatic ore fluids when the granitic magmas intruded, then precipitated as the ore sulfides.

Reaction rates of natural orpiment oxidation at 25 to 40°C and pH 6.8 to 8.2 and comparison with amorphous As 2S 3 oxidation

The oxidation rate of natural orpiment from Carlin-type deposits was measured at 25 to 40°C in a mixed flow reactor as a function of pH (6.8 to 8.2) and dissolved oxygen concentration (6.4 to 17.4 ppm) with a starting ionic strength of 0.01 M NaCl. All experiments ran for approximately 30 h, where steady-state conditions were reached after 20 h at a flow rate of 10 mL/min. The stoichiometric ratio of As/S was observed once steady state was reached. The rate law of orpiment oxidation is as follows: R=10 −11.77(±0.36)[ DO] 0.36(±0.09)[H +] −0.47(±0.05), where R signifies the rate of orpiment destruction (mol m −2 s −1), [DO] is the concentration of dissolved oxygen (M), and [H +] is the concentration of proton (M). The activation energy for the orpiment oxidation by dissolved oxygen at a temperature range of 25 to 40°C is 59.1 kJ/mol. Oxidation reactions of orpiment show incomplete oxidation of arsenic and sulfide in solution. At a pH range of 6.8 to 8.2, As(III) exists as H 3AsO 3 and As(V) is present as HAsO 4 2− and H 2AsO 4 −. Sulfite, sulfate, and thiosulfate are present as small fractions of total sulfur. The possible major sulfur species are intermediate oxidation state species. The oxidation rate of natural orpiment oxidation is slightly lower by a factor of 0.002 to 0.560 than that of As 2S 3(am) at the considered pH 7 to 10 and DO concentrations of 1 to 10 ppm. The dependence factors on pH for natural orpiment oxidation are lower by a factor of 0.37 compared with As 2S 3(am). However, the calculated activation energy is much larger for natural orpiment than As 2S 3(am) by a factor of 3.5. As(III) and As(V) are the major products for both As 2S 3(am) and natural orpiment oxidation along with intermediate sulfur species. The rate of orpiment oxidation increases with pH and results in an increase in the release of As. In mining-impacted environments with alkaline waters, as may be found in carbonate-hosted ore deposits, the natural attenuation of As oxyanions by sorption to oxide/hydroxide mineral surfaces is minimized because of a negative surface charge at a higher pH range. Thus, As concentrations may increase in mining-impacted waters at higher pH values (>8).

Hydrogeologic modeling of the genesis of carbonate-hosted lead-zinc ores

Carbonate-hosted lead–zinc ore deposits in the Mississippi Valley region of North America and in the central midlands region of Ireland provide good examples where ancient groundwater migration controlled ore formation deep within sedimentary basins. Hydrogeologic and geochemical theories for ore genesis are explored in this paper with mathematical models that allow for complex permeability fields in two or three dimensions, hydrothermal flows in fault systems, and coupled effects of geochemical reactions. The hydrogeologic framework of carbonate-hosted ores is analyzed with the aim of developing a quantitative understanding of the necessary and sufficient processes required to form large ore deposits. Numerical simulations of basin-scale hydrodynamics and of deposit-scale reactive flow are presented to demonstrate the processes controlling low-temperature Pb–Zn ore genesis in two world-class ore districts, in southeast Missouri, USA, and central Ireland.

Lead isotope systematics of epigenetic lead-zinc mineralization in the western part of the Rheinisches Schiefergebirge, Germany

In the western part of the Rheinisches Schiefergebirge three different types of epigenetic lead-zinc vein mineralization in Paleozoic rocks can be distinguished: 1. Syntectonic Variscan veins, 2. post-Variscan (Saxonian) veins mainly in Paleozoic siliceous clastic rocks, 3. post-Variscan carbonate-hosted mineralization in the Aachen-Stolberg area. Ore impregnations occur in the Triassic Buntsandstein (Bunter sandstone) and Muschelkalk of the Maubach-Mechernich triangular depression covering the Paleozoic rocks. Data points define two distinct populations in both lead isotope diagrams and thus indicate two major Variscan and post-Variscan mineralization events. The lead isotope pattern of the Paleozoic sedimentary rocks bears good evidence that this thick rock sequence may be the main source of metals for the mineralization. The metals were mobilized at deeper levels by saline fluids at different times. There are no direct indications for remobilization of the older Variscan vein ore deposits. The sandstone- and carbonate-hosted ore impregnations of Maubach-Mechernich have a similar lead isotope pattern to the post-Variscan mineralization in the Paleozoic sedimentary basement.

A precise 232Th- 208Pb chronology of fine-grained monazite: Age of the Bayan Obo REE-Fe-Nb ore deposit, China

We have obtained precise Th-Pb internal isochron ages on monazite and bastnaesite for the world's largest known rare earth elements (REE)-Fe-Nb ore deposit, the Bayan Obo of Inner Mongolia, China. The monazite samples, collected from the carbonate-hosted ore zone, contain extremely small amounts of uranium (less than 10 ppm) but up to 0.7% ThO 2. Previous estimates of the age of mineralization ranged from 1.8 to 0.255 Ga. Magnetic fractions of monazite and bastnaesite samples (<60-μm size) showed large ranges in 232Th 204Pb values (900–400,000) and provided precise Th-Pb internal isochron ages for paragenetic monazite mineralization ranging from 555 to 398 Ma within a few percent error (0.8% for two samples). These results are the first indication that REE mineralization within the giant Bayan Obo ore deposit occurred over a long period of time. The initial lead isotopic compositions (low 206Pb 204Pb and high 208Pb 204Pb) and large negative ϵ Nd values for Bayan Obo ore minerals indicate that the main source(s) for the ores was the lower crust which was depleted in uranium, but enriched in thorium and light rare earth elements for a long period of time. Zircon from a quartz monzonite, located 50 km south of the ore complex and thought to be related to Caledonian subduction, gave an age of 451 Ma, within the range of monazite ages. Textural relations together with the mineral ages favor an epigenetic rather than a syngenetic origin for the orebodies. REE mineralization started around 555 Ma (disseminated monazite in the West, the Main, and south of the East Orebody), but the main mineralization (banded ores) was related to the Caledonian subduction event ca. 474-400 Ma.

Metallogenic evolution in Wales: constraints from lead isotope modelling

Galena has been collected from different styles of mineralization throughout Wales. Galenas from the Ordovician volcanogenic mineralization at Parys Mountain, north Wales, give highly variable lead isotope ratios, which could have been produced either by a two-stage history or by the mineralizing fluids interacting and mixing with radiogenic lead derived from uranium-rich upper crust. The variation in the lead isotopic ratios of galena from veins cutting lower Palaeozoic sediments is considered to be due to separate periods of mineralization during the early Devonian and early Carboniferous. The most likely source for this mineralization is the thick sequence of lower Palaeozoic basinal mudstones. Both the disseminated galena in Mesozoic sedimentary rocks and galena from veins within the underlying Carboniferous Limestone give Triassic and Jurassic model lead ages, which agree with mineralization ages deduced from geological considerations. It is suggested that the source for this lead mineralization is the underlying Carboniferous shales. These and other galenas from Wales have significantly different isotope ratios to those from the Irish carbonate-hosted ore deposits, which would indicate that the mineralizing fluids had either different sources or evolutionary histories.

Carbonate-hosted ore deposits and the British Geological Survey

Carbonate-hosted ore deposits and the British Geological Survey

Mineralogy and paragenesis of the cupriferous deposits of the Acton Vale-Upton sector, Klippen Belt, Quebec

Mineralogical and paragenetic studies of the metallic and nonmetallic constituents of the carbonate-hosted cupriferous ores of the Acton Vale-Upton sector, Klippen Belt, Quebec, have revealed the following. The deposits are characterized by a simple mineralogy and a complex paragenesis. Several generations of pyrite and chalcopyrite are associated with sphalerite, galena, pyrrhotite, covellite, bornite, idaite, djurleite, malachite, azurite, Fe oxides, and minor barite. The deposits are characterized by three discrete mineral assemblages which are composed of syndiagenetic minerals, epigenetic minerals, and supergene minerals. They are hosted by concordantly interbedded lithologies that have been hydrothermally altered by intrusions. The deposits are characterized by massive lenticular bodies, stockworks, vugs, veins, and by cockade and replacement textures, solution collapse breccias, and karst phenomena. The deposits have been enriched in recent times by supergene processes. Considering that the lithostratigraphic sequence constitutes an ideal structural trap for ascending mineralizing fluids, it is the authors' opinion that the deposits are unconventional epigenetic, carbonate-hosted, Cu-dominant and/or Pb-Zn-Ba bodies which in their original form were too low grade to be economic. They required postdepositional remobilization and concentration to upgrade their protores. Based on the assumption that the ores were derived from the expulsion of metal-rich formation waters during compaction and that they were, at one point, contaminated and set in motion by magmatic solutions emanating from rising plutons of post-Taconic age, it is inferred that the thermal energy necessary to remobilize the ores was provided by the intrusions of the Acton Vale-Upton sector.